Magnetic recording media having a magnetic recording layer containing a cellulose derivative, a polyurethane and a polyisocyanate are described in, for example, U.S. Pat. Nos. 3,242,005 and 3,630,771. The conventional magnetic recording media suffer the occurrence of skew distortion.
"Skew distortion" refers to a video tape defect in which images are deformed and distorted because the magnetic tape expands or contracts in the runnning direction, and consequently the length of the track to be recorded is changed. In order to prevent skew and to improve the durability of such a tape, after a magnetic layer is coated on a support, the resulting coated layer is generally subjected to heat treatment at a relatively high temperature. However, such heat treatment deteriorates the surface smoothness of the support due to heat shrinkage and thereby deteriorates the surface properties of the magnetic recording medium itself.
In view of this problem, it has been proposed in Japanese Patent Application (OPI) No. 15927/82 (as used herein, "OPI" refers to a published, unexamined Japanese Patent Application") to reduce the heat shrinkage of the support to thereby reduce skew. However, if a coated layer is subjected to heat treatment at a high temperature for a short period of time to accelerate the hardening reaction, this method has the disadvantage that chroma S/N is reduced. Further, when the heat treatment is carried out at a relatively low temperature, still life is often reduced.